1. Technical Field
This device relates to control systems for pneumatic cylinders that have heretofore utilized proximity switches and separate pressure sensing valves to react to the position of the piston during operation as an end to stroke detection.
2. Description of Prior Art
Prior art devices of this type have relied on a variety of different switching and sensing devices to monitor pneumatic and hydraulic cylinder positions and control, see for example U.S. Pat. Nos. 3,680,583, 3,691,902, 4,275,793, 4,819,541 and 4,936,143.
In U.S. Pat. No. 3,680,583 an automatic four-way hydraulic operated valve is disclosed that uses the pressure build-up within the cylinder and releases same using a single spool package type unit.
U.S. Pat. No. 3,691,902 discloses a cylinder and plunger control valve that senses the true end of stroke of a piston in a cylinder.
U.S. Pat. No. 4,275,793 claims a control system for rock drills wherein location of the drill to the control valve is accomplished by measuring the pressure and flow rate of hydraulic fluid to the motor with pressure responsive switches.
U.S. Pat. No. 4,819,541 on a control valve for double acting pneumatic drive cylinders adjust airflow through variable orifices and check valves creating a restrictive flow path in one direction to prevent rebound with strong holding pressure.
U.S. Pat. No. 4,936,143 is directed to cylinders having piston position measuring configurations in which an ultrasonic transducer is used to determine the piston's position within the cylinder.